tion and strategy about how to get from place A to place B. Navigation is the term often used in this context.

5.2.2 Assistive Technology Systems for the Travel Process

There have been considerable advances in the available approaches to developing assistive technology systems. In particular, there is increasing recognition of the importance of the involvement of end-users in all stages of the design process and increasing use of human-centred, user-centred and participative design approaches. Assistive technology researchers can also draw on the social model of disability and the framework for modelling assistive technology presented in Chapter 1. In the past there has been a tendency to focus on technical aspects of travel by blind and visually impaired people and ignore the human dimension. This led to the application of (new) advanced technologies without consideration of the wider context. Success in developing (electronic) travel aids for blind and visually impaired people has been rather limited. Many of the devices have not gone beyond the prototype stage. Only relatively small numbers of the most successful electronic devices are in use and the long cane and guide dog (see Sections 5.4.1 and 5.5.1) are still the most widely used travel aids for blind and visually impaired people. This indicates a need for more research into the reasons for this lack of success to target future research and development in this area better. Possible reasons (which would require experimental verification) include the following:

•Excessive complexity, making devices difficult to learn and use, combined with a lack of training.

•High costs and a lack of research and development funding.

•Inappropriate appearance.

•Not meeting users’ needs.

•Awkward or heavy to carry.

•Not providing significantly greater functionality than the long cane.

From the user’s point of view, it is clearly advantageous to have one device that supports all travel activities. From the engineering design perspective, it is useful to have a categorisation of the different types of activities involved. This can be motivated by considering typical travel activities, for instance, travelling down an urban street (Figure 5.3).

Typical travel issues that can be identified from the street scene are as follows.

Obstacle avoidance

•Clear-path ahead: the need to have a clear forward path at chest height, at leg height (litter bin) at head height (tree branches).

•The need to have sufficient space at the sides to proceed: for instance, scaffolding or a wall at one side, a doorway or arch or a path that narrows need to be identified.

174 5 Mobility: An Overview

Figure 5.3. Obstacles, hazards and information in an urban street scene

•Path level changes: the need to identify path drop-offs, sudden path step-ups and down slopes and inclines.

Mobility: orientation and navigation

•Safe pavement position, safe path following.

•Safe traffic crossing for pedestrians.

•Route finding: finding and following the desired route.

•Indication that the destination has been reached or a desired object, such as a door or waste bin, found.

Environmental access: hazard minimization

•Safe traffic crossing for pedestrians.

•Indicators, for instance, of the locations of the ends of pavements and traffic crossings.

•Street furniture being sited to avoid it becoming an obstacle and hence a hazard to pedestrians.

Environmental access: information and signs

•Information about location, access to street signage, public transport information and other public notices.

Travel for blind people can be facilitated by both the use of assistive technology and accessible environmental design. For instance, street furniture, such as bins and lampposts, should be positioned so that it does not present an obstacle. However, assistive devices will still be required, to detect people and any street furniture that still presents an obstruction. In general, environmental access will

be promoted by accessible design, whereas both accessible design and assistive technology will support mobility.

Although some attention is now being given to an integrated approach to the development of assistive technology and the overcoming of infrastructural barriers, this has not yet had a significant impact on work in the area. Therefore, most researchers are still focussing on the development of assistive devices for either obstacle avoidance or orientation whilst there is a separate body of work on removing barriers and making environments more accessible to blind and visually impaired people.

Most mobility (obstacle avoidance) and orientation devices carry out the following two functions:

1.Obtaining near-space or far-space information

2.Providing this information to the user in an appropriate form

Most of the research in the area has concentrated on different methods for obtaining information and there has been less research effort on communicating this information to the end-user. This may be one of the reasons why a number of devices have been unsuccessful. Communicating information to the end-user raises the following issues, many of which still require further investigation:

•The choice of sensory modality, that is, touch or hearing. For some visually impaired people it might be possible to process the information to enable them to receive it visually. For instance, this could include presenting information so that it could be detected by central vision and therefore used by visually impaired people who only have central vision.

•The provision of information in a way that does not interfere with the use of sensory environmental information. For instance, speech or sounds should be provided by an ear phone to one ear only, so as not to impede the detection of auditory environmental cues.

•The need for training, including in the processing of complex tactile or auditory information and whether this training is required from an early age. Currently the processing capabilities of touch and hearing limit the information that can be provided. However, it is possible that appropriate training, particularly if carried out at an early age, would overcome this limitation or at least reduce its impact.

•The amount of information provided. Most existing devices provide basic information, for instance on whether or not there is an obstacle, rather than complex information which would give the user an overview of the scene.

A consequence of this type of simple decomposition of the travel task is that in the past, assistive technology engineers have devised ad hoc solutions to some of these individual problems in the separate categories: (1) obstacle avoidance assistive technology and (2) orientation and navigation assistive technology. It is only in more recent years that the idea of taking an integrated approach to the development of assistive technology solutions has been proposed and in some cases implemented.

176 5 Mobility: An Overview

5.2.2.1 Categorisation of Travel Aids

There are a number of different categorisations of travel aids, which can be stated as follows:

1.Into primary and secondary aids based on whether the device can be used on its own or is used to supplement another device:

•Primary aids. These are used on their own to deliver safe mobility. A typical example is the long cane.

•Secondary aids. These devices are used to supplement a primary device. However, they have not been designed to deliver safe mobility when used on their own. A hand-held ultrasonic torch device for obstacle detection is an example of a secondary aid that could be used to augment the use of a long cane.

2.Based on the functionality of the device:

•Mobility devices that support obstacle avoidance.

•Orientation and navigation devices that provide information on landmarks and support route finding.

•Environmental access assistive technology.

•Devices which support object finding.

3.Based on the technology used to obtain the environmental information:

•Ultrasonic.

•Infrared.

•Camera.

•Global positioning system (GPS).

•Mobile phone technology.

4.Based on the way information is provided to the user:

•Tactile, generally by vibration.

•Speech.

•Sounds of varying loudness and pitch.

•Musical tones.

5.Based on how the device is carried:

•Cane.

•Other hand-held device.

•Carried in pocket.

•Carried in back pack.

To give a uniform presentation to the many different assistive technology devices and applications it is useful to use the comprehensive assistive technology (CAT) model. This provides a very general framework for the development and comprehension of assistive technology. The assistive technology system block diagram is